This invention relates to ink-jet printing.
In drop-on-demand ink-jet printing, for example, a particular print head may have 256 jets in four groups of 64 jets each. The four groups are formed in four respective pieces of piezoelectric material.
Printing occurs in print cycles. In each print cycle, a fire pulse (say, 150 volts) is applied to all of the 256 jets at the same time and enabling signals are sent only to those of the jets that are to jet ink. In some print heads, the ink jet orifices are aligned in a row, and a print cycle corresponds to a print line.
The volume of the drop of ink that is produced by the fire pulse depends on the properties of each ink-jet. Some applications, such as printing color films for liquid crystal display (LCD) panels, require a degree of uniformity of the drop volume sizes applied by the ink-jets.
One way to cause the ink-jets to have uniform drop volumes is to trim or offset the common fire pulse voltage by an appropriate amount at each ink-jet. Another approach is described in U.S. patent application Ser. No. 5,790,156.
In general, in one aspect, the invention features, during a print cycle, delivering fire pulses of different profiles to ink-jets of a print head, and enabling selected ones of the inkjets in coordination with the occurrence of selected ones of the fire pulses to control at least one characteristic of drops that are jetted by the respective ink-jets.
Implementations of the invention may include one or more of the following features. The selected ones may be all or fewer than all of the ink-jets in the print head. The fire pulses of different profiles may be delivered in sequence, and the same sequence may be repeated in successive print cycles. The profiles may differ in voltage and/or in duration. The characteristic of the drops that is controlled may include the drop volume and/or the drop velocity. The pulses and ink-jets may be selected to cause the volumes (and/or velocities) of drops jetted by the ink-jets in the line to be essentially uniform. The substrate may be a film that is to be incorporated into an LCD panel. In various aspects, the invention features enabling selected ones of the ink-jets in coordination with selected ones of the fire pulses in a manner that said selected ink-jets are enabled during multiple fire pulses within a print cycle.
In general, in another aspect, the invention features apparatus that includes a print head having ink-jets, and a controller coupled to the print head and configured to (a) deliver fire pulses of different profiles to ink-jets of a print head in a print cycle, and (b) enable selected ones of the ink-jets in coordination with the occurrence of selected ones of the fire pulses to control at least one characteristic of drops that are jetted by the respective ink-jets.
In general, in another aspect, the invention features a method in which (a) a substrate is positioned at successive locations relative to a print head having ink-jets for printing in a corresponding succession of print cycles, (b) during each print cycle, fire pulses of different profiles are delivered to ink-jets of a print head, and (c) selected ones of the ink-jets are enabled in coordination with the occurrence of selected ones of the fire pulses to control at least one characteristic of drops that are jetted by the respective ink-jets.
In general, in another aspect, the invention features a method in which (a) values of a characteristic of drops jetted by an ink-jet in a print head are associated with different profiles of fire pulses that yielded the drops, and (b) respective ink-jets are controlled to jet drops having desired values by selecting different profiles of a fire pulse within a print cycle.
In another aspect, the invention features a method of controlling grayscale, including during a print cycle, delivering fire pulses of different profiles to ink-jets of a printhead, the different profiles being associated with different ink volumes jetted by said ink-jets. The fire pulses are selected according to desired grayscale level by determining the cumulative ink volume resulting from multiple fire pulses. Selected ones of the ink-jets are enabled in coordination with the occurrence of the fire pulses to control the ink volume that is jetted by the respective ink-jets during the print cycle.
In another aspect, the invention features an apparatus including a printhead having ink-jets, and a controller coupled to the printhead and configured to (a) deliver fire pulses of different profiles to multiple ink-jets of a printhead in a print cycle, said different profiles being associated with different ink volumes jetted by said ink-jets, (b) select a set of said fire pulses corresponding to said desired grayscale levels by determining the cumulative ink volume resulting from multiple fire pulses, and (c) enable selected ones of the ink-jets in coordination with the occurrence of one or more of the fire pulses in the set to control the ink volume jetted by the respective ink-jets during the print cycle.
Implementations may include one or more of the following. The ink volume for multiple jets is determined as a function of pulse profile. The jets are sorted into a group of common grayscale level and enabling said group during common fire pulses. The drop volume difference between jets in said group is about xc2x110% or less. At least three fire pulses are delivered. At least two fire pulses are enabled.
The aspects are preferably used to control drop uniformity between jets by determining the drop volume or other characteristic for each jet as a function of fire pulse profile and controlling them accordingly to fire droplets of substantially equal volume or other characteristics. The control may include enabling multiple pulses to fire multiple drops from a given jet during a print cycle. In addition, the drop volume control can be used to adjust and control grayscale of an image. For example, the cumulative ink volume from multiple pulses can be determined and the range and resolution of the grayscale can be enhanced.
Other advantages and features will become apparent from the following description and from the claims.